linux-kernel - Re: [PATCH RFC] delayacct: add memory reclaim delay in get_page_from

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Message-Id: <20230902164454.30dda58820ced683849b45cb@linux-foundation.org>
Date:   Sat, 2 Sep 2023 16:44:54 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     "liwenyu01@...ibili.com" <liwenyu01@...ibili.com>
Cc:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "wangyun@...ibili.com" <wangyun@...ibili.com>
Subject: Re: [PATCH RFC] delayacct: add memory reclaim delay in
 get_page_from_freelist

On Thu, 31 Aug 2023 07:26:20 +0000 "liwenyu01@...ibili.com" <liwenyu01@...ibili.com> wrote:

> reclaim of the task in do_try_to_free_pages(). In systems with NUMA
> open, some tasks occasionally experience slower response times, but the
> total count of reclaim does not increase, using ftrace can show that
> node_reclaim has occurred.
> 
> The memory reclaim occurring in get_page_from_freelist() is also due to
> heavy memory load. To get the impact of tasks in memory reclaim, this
> patch adds the statistics of the memory reclaim delay statistics for
> __node_reclaim().
> 
> ...
>
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -8010,6 +8010,7 @@ static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned in
> 
>         cond_resched();
>         psi_memstall_enter(&pflags);
> +       delayacct_freepages_start();
>         fs_reclaim_acquire(sc.gfp_mask);
>         /*
>          * We need to be able to allocate from the reserves for RECLAIM_UNMAP
> @@ -8032,6 +8033,7 @@ static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned in
>         memalloc_noreclaim_restore(noreclaim_flag);
>         fs_reclaim_release(sc.gfp_mask);
>         psi_memstall_leave(&pflags);
> +       delayacct_freepages_end();
> 
>         trace_mm_vmscan_node_reclaim_end(sc.nr_reclaimed);

__node_reclaim() calls shrink_node() which at some point will call
do_try_to_free_pages() (yes?), which calls delayacct_freepages_start().

So we're effectively nesting calls to delayacct_freepages_start(),
which isn't designed for that?